CN1205484C - System and method for determining the location of a wireless CDMA transceiver - Google Patents

Abstract

Apparatus and method for determining a mobile wireless transceiver. The present invention combines GPS positioning and wireless communication technology to obtain accurate positioning in dense urban and other environments when the line of sight of satellites is not clear. The device and invention of the present invention use signals from only two GPS satellites (60, 70, 80, 90) and ground base stations providing services. In general, the method of the invention comprises receiving at a base station (10) a first signal transmitted from a first GPS satellite and a second signal transmitted from a second GPS satellite. The mobile unit's transmitter (200) and receiver (100) are adapted to receive these GPS signals and in response thereto send a third signal to the base station. The base station (10) receives the third signal and uses it to calculate the location of the wireless unit (20).

Description

System and method for determining the location of a wireless CDMA transceiver

field of invention

The present invention relates to communication systems. In particular, the present invention relates to systems and techniques for determining the location of a wireless transmitter in a code division multiple access system.

Description of related technologies

Location technology in wireless networks is booming as regulatory forces and communications companies look to increase revenue by differentiating themselves from those offered by competitors. Additionally, in June 1996, the Federal Communications Commission (FCC) ordered support for enhanced emergency 911 (E-911) services. Phase I of this order requires sector and cell information to be set back to the PSAP (Public Safety Answering Point) agent. Phase II of the Act requires that the location of the cellular transceiver be sent back to the PSAP. In order to comply with the FCC order, a total of 77,000 cell sites must be equipped with automatic positioning technology before 2005.

Many technologies are considered to be capable of automatic positioning. One known technique involves measuring the difference in arrival times of signals from multiple cell sites. These signals are triangulated to extract location information. Unfortunately, this technique requires a high concentration of cells and/or increased transmission power of cells to be effective. This is due to the fact that in a typical CDMA system, each phone transmits with only enough power for the signal to reach the nearest cell site. Where triangulation requires communication with at least three cells, the concentration of cells must be increased or the signal power per radio must be increased.

In any case, each scheme has significant disadvantages. The cost of increasing the number of district stations is high. The increase in signal power increases the weight and cost of each wireless unit and increases the likelihood of mutual interference between wireless users. Furthermore, triangulation schemes cannot provide the accuracy required by the FCC order.

Another known method involves adding GPS (Global Positioning System) functionality to cellular phones. Although this method significantly increases the cost and weight of the wireless unit, requires line-of-sight to four satellites, and is somewhat slow, it is the most accurate method to support positioning services.

To speed up the process, a third method sends help information to the wireless unit, which instructs the wireless unit where in the frequency domain of the GPS carrier it should search. Most GPS receivers use something called a GPS satellite almanac to minimize the number of times the receiver searches in the frequency domain for signals from visible satellites. The almanac is a 15,000-bit block of coarse ephemeris and time model data for the entire constellation. Information in the almanac about satellite positions and time of day is only approximate. Without an almanac, the CPS receiver must perform the widest possible frequency search to acquire satellite information. Additional processing is required to obtain additional information, which facilitates acquisition of other satellites.

The signal acquisition process can take several minutes due to the large number of frequency bins that need to be searched. Each frequency segment has a center frequency and a predetermined width. The availability of almanacs reduces the uncertainty in the satellite Doppler, thus reducing the number of frequency bands that must be searched.

Satellite almanacs can be extracted from GPS navigation messages or sent on the downlink (forward) link as data or signaling messages to the receiver. When this information is received, the receiver performs GPS signal processing to determine its position. While this method is somewhat faster, it requires line of sight to at least 4 satellites. This is problematic in urban environments.

Therefore, there remains a need in the art for a fast, accurate and inexpensive system and technique for locating cellular units.

Summary of the invention

The system and method of the present invention for determining the location of a wireless transceiver fulfills this need in the prior art. In general, the method of the present invention is a hybrid method of determining position using ranging information from terrestrial systems and ranging information from GPS satellites. This information is combined to allow the location of the wireless unit to be determined quickly and reliably. The method of the present invention includes the wireless unit receiving a first signal transmitted from a first GPS satellite, a second signal transmitted from a second GPS satellite, and a third signal transmitted from a third satellite. The wireless unit is adapted to receive such a GSP signal and to transmit a fourth signal to the base station in response thereto. The base station receives the fourth signal, corrects for a clock bias imposed on the fourth signal using a round trip delay between the base station and the wireless unit, and uses the unbiased fourth signal to calculate the position of the wireless unit.

In a particular implementation, the base station sends assistance information to the wireless unit. The wireless unit uses the assistance information to quickly acquire the signals transmitted by the first, second and third satellites. Aiding information is derived from information collected by the base transceiver subsystem (BTS) providing service to the wireless unit and includes satellite identification information, Doppler shift information and values representing the distance between the base station and each satellite, and A search window size associated with each satellite, where the search window size is calculated based on the round trip delay between the wireless unit and the base station and the elevation angle of each satellite.

As soon as the wireless unit acquires the signals transmitted by the first, second and third satellites, the wireless unit calculates the range between the wireless unit and each satellite pm1, pm2 and pm3 respectively. The ranging information is sent back to the base station together with information about the measurement time. In a CDMA implementation, the time at which the wireless unit transmitted the fourth signal to the base station is known to the base station. The delay in receiving the fourth signal indicates to the base station the distance between the wireless unit and the base station. In addition, this delay provides a means of correcting the absolute time of the wireless unit.

A device external to the mobile device, such as a base station controller or some other entity related to the cellular infrastructure, utilizes information known to the serving base station, such as its location, first, second and The position of the third satellite and the distance between the wireless unit and the base station) calculate the position of the wireless unit. This can be done by finding the first sphere with radius cp1 around the first satellite, the second with radius cp2 around the second satellite and the third with radius cp3 around the third satellite and the fourth with radius cp6 around the base station sphere, where c is the speed of light, p1 is the pseudorange associated with the first satellite and wireless unit, p2 is the pseudorange associated with the second satellite and wireless unit and p3 is the pseudorange associated with the third satellite and wireless unit Pseudorange.

Note that the proposed method requires measurements from only two satellites and one base station if line-of-sight (not multipath) exists between the wireless unit and the base station. Additional information from another base station (if available) can be used to further reduce the number of satellites. Furthermore, only two satellites and one base station are required where only two-dimensional positions are required.

A key advantage of this method over other known GSP methods is the speed with which the wireless unit can determine pseudoranges. Since the serving base station has its own GPS receiver and also knows the pseudoranges of all satellites being tracked relative to the serving base station position, the search window center and the search window can be determined for each satellite being tracked size. This information is sent to the wireless unit to increase the speed of the search process.

That is, the clock carried by each GPS satellite controls the timing at which the satellite broadcasts ranging signals. Each such clock is synchronized with the GPS system time. The base station also contains a clock synchronized with the GPS system time. The wireless unit synchronizes its clock to GPS time with a delay corresponding to the one-way delay between the base station and the wireless unit. Timing information is embodied in the satellite ranging signal, which enables the wireless unit to calculate when to transmit a signal from a particular satellite. By recording the time the signal was received, the distance (range) from the satellite to the wireless unit can be calculated. As a result, the location of the wireless unit is a sphere centered at the satellite location with a radius equal to the calculated range. If the measurements are taken simultaneously using the ranging of two other satellites, then the wireless unit will be somewhere on the surface of the three spheres. The three balls intersect at two points, however, only one point is the correct wireless user location. Candidate positions are mutual mirror images relative to a plane containing the three satellites.

In the optimal mode, the base station of the present invention identifies the three best GPS satellites to use to determine the location of the wireless unit at a given moment. This information is sent to the wireless unit to facilitate search operations performed by the wireless unit.

In one embodiment, the wireless unit may have several modes of operation:

(1) A hybrid model using information from the wireless system infrastructure and GPS satellites;

(2) stand-alone (standard or traditional) GPS mode;

(3) Auxiliary stand-alone GPS mode;

(4) Inverted differential GPS mode; and

(5) Assisted and inverse differential GPS modes.

According to one aspect of the present invention, there is provided 1. A system for determining the position of a mobile wireless transceiver, characterized in that it includes:

base station; means for respectively calculating Doppler shifts of signals transmitted from first, second and third satellites relative to said base station; respectively calculating a first set of pseudoranges of first and second satellites relative to said base station means for transmitting satellite identification information, Doppler shift information, and the pseudorange information between the base station and the wireless transceiver; located at the wireless transceiver for receiving information from the base station means for said satellite identification information, Doppler shift information and said pseudorange information; located at said mobile radio transceiver for identifying said satellite at time T using said information received from said base station means for a second set of pseudoranges between the transceiver and said first and second satellites, respectively; located at said mobile radio transceiver for placing said transceiver between said first and second satellites, respectively The second set of pseudoranges and the time information at time T are sent to the base station together; and means located at the base station for calculating in response to the second set of pseudoranges and the time information at time T means for the location of the wireless transceiver.

In the above system, said means at said base station for calculating the position of said wireless transceiver responsive to said second set of pseudoranges and said time information of time T comprises determining said wireless transceiver distance The distance means of the base station.

In the above system, said means at said base station for calculating the location of said wireless transceiver includes means for utilizing a distance of said wireless transceiver from said base station in calculating the location of said wireless transceiver.

In the above system, means are included at said base station for identifying the two best positioned satellites.

In the above system, means are included for switching said mobile radio transceiver from a first mode affecting voice/data communication to a second mode determining its position.

In the above system, said means at said base station for calculating the position of said wireless transceiver comprises: using said second set of pseudoranges to calculate the distance between said first and second satellites and said base station, respectively. means for a third set of pseudoranges between, and using the known positions of said two satellites at time T, said position of said base station, said third set of pseudoranges, and signals sent from said mobile radio transceiver to means for determining said position of said wireless transceiver by delaying the time of arrival of said base station signal.

In the above system, said means for calculating said position of said transceiver comprises finding a first sphere of a first radius around a first of two satellites, a second radius around a second of two satellites, means the intersection of a second sphere of radius and a third sphere of third radius surrounding the base station.

In the above system, said means for calculating said position of said transceiver comprises finding a first sphere of a first radius around a first of two satellites, a second radius around a second of two satellites, means the intersection of a second sphere of radius and a third sphere of third radius surrounding the base station.

According to another aspect of the present invention, there is provided a system for determining the position of a mobile wireless transceiver, comprising: a base station; means located at said base station for identifying first and second Global Positioning System satellites; means for calculating Doppler shifts of signals transmitted from the first and second satellites relative to the base station, respectively; calculating the first set of pseudoranges of the first and second satellites relative to the base station, respectively means; means for transmitting satellite identification information, Doppler shift information, and said pseudorange information from said base station to said wireless transceiver; located at said wireless transceiver for receiving said means for satellite identification information, Doppler shift information and said pseudorange information; located at said mobile radio transceiver for identifying said transceiver at time T using said information received from said base station means for said second set of pseudoranges between said first and second satellites, respectively; located at said mobile radio transceiver for placing said transceiver between said first and second satellites, respectively The second set of pseudoranges and the time information at time T are sent to the base station together; means for the location of the wireless transceiver, the computing means comprising: means for determining the distance of the wireless transceiver from the base station; and using the distance of the wireless transceiver from the base station in calculating the location of the wireless transceiver device.

In the above system, means are included for switching said mobile radio transceiver from a first mode affecting voice/data communication to a second mode determining its position.

In the above system, said means at said base station for calculating the position of said wireless transceiver comprises: using said second set of pseudoranges to calculate the distance between said first and second satellites and said base station, respectively. means for a third set of pseudoranges between them; and using the known positions of said first and second satellites at time T, the position of said base station, the third set of pseudoranges and the signals sent from said mobile radio transceiver to said means for determining the location of said radio transceiver based on the time delay of arrival of signals from said base station.

In the above system, said means for calculating the position of said wireless transceiver comprises finding a first sphere of a first radius around a first of two satellites, a second radius around a second of two satellites means the intersection of the second sphere and a third sphere of a third radius around the base station.

In the above system, said means for calculating the position of said wireless transceiver comprises finding a first sphere of a first radius around a first of two satellites, a second sphere of a second radius around a second of two satellites Means the intersection of two spheres and a third sphere of a third radius around the base station.

According to still another aspect of the present invention, there is provided a method for determining the position of a mobile radio transceiver, characterized in that it comprises the steps of: calculating Doppler deviations of signals transmitted from first and second satellites with respect to a base station, respectively respectively calculate the first set of pseudoranges of the first and second satellites relative to the base station; send satellite identification information, Doppler shift information and the pseudorange information from the base station to the radio a transceiver; receiving at said transceiver said satellite identification information, Doppler shift information and said pseudorange information from said base station; using said information received from said base station to identify The second group of pseudo-ranges between the transceiver and the first and second satellites; the second group of pseudo-ranges and sending time information together at time T to said base station; and calculating a position of said wireless transceiver in response to said second set of pseudoranges and said time information.

In the above method, said step of calculating the position of said radio transceiver in response to said second set of pseudoranges and said time information at time T comprises the step of determining a distance of said radio transceiver from said base station .

In the above method, said step of calculating the location of said wireless transceiver includes the step of utilizing the distance between said wireless transceiver and said base station in calculating the location of said wireless transceiver.

In the above method, the step of identifying the two best positioned satellites is included.

In the above method, the step of switching said mobile radio transceiver from a first mode affecting voice/data communications to a second mode determining its location.

In the above method, said step of calculating the position of said wireless transceiver comprises the step of: using said second set of pseudoranges to calculate a third distance between said first and second satellites and said base station, respectively. a set of pseudoranges; and determining said radio transceiver using the known positions of said two satellites at time T, a third set of pseudoranges, and a time delay of arrival of a signal transmitted from said mobile radio transceiver to said base station s position.

In the above method, said step of calculating the position of said wireless transceiver comprises finding a first sphere of a first radius around a first of two satellites, a second sphere of a second radius around a second of two satellites Step of the intersection of the two spheres and a third sphere of a third radius around the base station.

In the above method, said step of calculating the position of said wireless transceiver comprises finding a first sphere of a first radius around a first of two satellites, a second sphere of a second radius around a second of two satellites Step of the intersection of the two spheres and a third sphere of a third radius around the base station.

Description of drawings

1 is a diagram illustrating an example implementation of base stations and wireless units of a wireless (CDMA) communication system.

Figure 2 is a block diagram of an example CDMA cellular telephone system.

Figure 3 is a simplified representation of a base station constructed in accordance with the teachings of the present invention.

Figure 4 is a block diagram of a wireless unit of the system for determining the location of a wireless CDMA transceiver of the present invention.

5 is a block diagram of an exemplary implementation of the receiver, control signal interface, digital IF, and radio demodulator circuit portions of the wireless unit of the present invention.

Figure 6 is a diagram of a functional model for determining the location of a wireless unit.

Figure 7 shows the computation of the search window size and center in the time domain.

FIG. 8 is a diagram illustrating local clock offset correction.

Detailed description of the invention

Example embodiments are described with reference to the drawings.

While the present invention has been described with reference to example embodiments for particular applications, it should be understood that the invention is not limited thereto. Those familiar with the art and reading the disclosure herein will recognize additional modifications, applications, and embodiments within the scope of the invention and additional fields in which the invention is particularly useful.

1 is a diagram illustrating an example implementation of a base station 10 and a wireless unit 20 of a wireless (CDMA) communication system. The communication system is surrounded by buildings 40 and obstructions 50 on the ground. The base station 10 and the wireless unit 20 are arranged in a GPS (Global Positioning System) environment, which has several GPS satellites, four of which are shown in the figure, 60, 70, 80 and 90. Such GPS environments are known. See, eg, GPS Principles and Practice by Hofmann-Wellenhof, B. et al. (Second Edition, New York, NY: Springer-Verlag Wien, 1993). Those skilled in the art will appreciate that the present technology may be applied to other communication systems, such as Advanced Mobile Phone System (AMPS), Global System for Mobile Communications (GSM), etc., without departing from the scope of the present invention.

In a typical GPS application, at least 4 satellites are required for a GPS receiver to determine its position. In contrast, the present invention provides a method and apparatus for determining the location of the wireless unit 20 using only three GPS satellites, the round trip delay from the wireless unit to the serving base station 10, and the known location of the serving base station 10. In the case of direct line of sight, only two GPS satellites, the round-trip delay, and the known location of the base station 10 providing the service are required to locate the wireless unit 20 .

Figure 2 is a block diagram of a CDMA cellular telephone system. The system includes a Mobile Switching Center (MSC) 12 having a Base Station Control (BSC) 14 . The public switched telephone network (PSTN) 16 routes calls to/from the MSC 12 from telephone lines or other networks (not shown). MSC 12 routes calls from PSTN 16 to/from source base station 10 associated with first cell 19 and target base station 11 associated with second cell 21 . In addition, MSC 12 routes calls between base stations 10,11. The source base station 10 sends the call directly to the first wireless unit 20 in the first cell 19 via the first communication path 28 . Communication path 28 is a bidirectional link including forward link 31 and reverse link 32 . Typically, link 28 includes a traffic channel when base station 10 has established voice communication with wireless unit 20 . Although each base station 10, 11 is associated with only one cell, a base station controller usually manages or is associated with base stations in several cells.

When the wireless unit 20 moves from the first cell 19 to the second cell 21, the wireless unit 20 begins communicating with the base station associated with the second cell. This is generally referred to as "handover" to the target base station 11 . During a "soft" handover, the wireless unit 20 establishes a second communication link 34 with the target base station 11 in addition to the first communication link 28 with the source base station 10 . When the wireless unit 20 traverses into the second cell 21 and establishes a link with the second cell, the wireless unit may lose the first communication link 28 .

During a hard handover, the operation of the source and target base stations is generally sufficiently different that the communication link 34 between the source base stations must be lost before the link to the target base station can be established. For example, when the source base station is in a CDMA system using a first frequency band and the target base station is in a second CDMA system using a second frequency band, the wireless unit cannot maintain links to both base stations simultaneously because most wireless units Does not have the ability to tune to two different frequency bands at the same time. When the first wireless unit 20 moves from the first cell 19 to the second cell 21, the link 28 to the source base station 10 is lost and a new link with the target base station 11 is formed.

Figure 3 is a simplified representation of a base station 10 constructed in accordance with the teachings of the present invention. According to the embodiment shown in Fig. 3, the base station 10 is basically prior art. In another embodiment, the base station 10 includes additional functionality that allows the base station to determine the location of the wireless unit 20, as will be apparent from the description provided below. Conventional base station 10 includes a receive CDMA antenna 42 for receiving CDMA signals and a transmit CDMA antenna for transmitting CDMA signals. Signals received by antenna 42 are routed to receiver 44 . In practice, receiver 44 includes demodulators, deinterleavers, decoders and other circuits, as will be understood by those skilled in the art. The received signal is assigned to the appropriate channel associated with rate detector 60 . The control processor 62 uses the rate of the detection signal to detect speech. Control processor 62 switches the received frame to vocoder 64 via switch 63 if speech is detected in the received frame. Vocoder 64 decodes the variable rate encoded signal and provides a digitized output signal in response thereto. A digital-to-analog converter 65 and an output device such as a speaker (not shown) convert the digitized de-vocoded signal into speech.

An analog-to-digital converter 66 digitizes incoming speech from a microphone or other input device (not shown) and vocodes it by a vocoder encoder 68 . The vocoded speech is input to the transmitter 69. In practice, transmitter 69 includes modulators, interleavers and encoders, as is known in the art. The output of transmitter 69 is fed to transmit antenna 43 .

The conventional base station 10 is also provided with a GPS antenna 76 , a receiver 74 and a timing and frequency unit 72 . The timing and frequency unit accepts signals from the GPS engine of the GPS receiver and uses them to generate timing and frequency references to properly operate the CDMA system. Therefore, in many such CDMA systems, each cell site uses a GPS time base reference from which all timecritical CDMA transmissions (including pilot sequences, frames, and Walsh functions) are derived. Such conventional timing and frequency units and GPS engines are common in CDMA systems and are known in the art. Traditional timing and frequency units provide frequency pulses and timing information. Instead, the timing and frequency unit 72 of the present invention preferably also outputs the elevation angle, pseudorange, satellite identification (i.e., pseudonoise (PN) offset associated with each satellite), and Doppler offset associated with each satellite , thereby assisting the wireless unit 20 in acquiring satellites (ie, reducing the amount of time required to acquire satellites). Typically, this information is available in conventional timing and frequency units, but is generally neither needed nor provided to external devices. The additional information provided by timing and frequency unit 72 is sent to BSC 14, preferably in the same manner as is done with respect to frequency and timing information in conventional base stations.

FIG. 4 is a block diagram of wireless unit 20 according to one embodiment of the present invention. Wireless unit 20 preferably includes a bi-directional antenna 92 adapted to receive CDMA transmissions as well as GPS signals. In another embodiment of the invention, separate antennas may be used to receive and transmit GPS signals, CDMA signals and other signals, such as another system signal. Antenna 92 preferably feeds duplexer 94 . The duplexer 94 preferably feeds the receiver 100, and preferably the transmitter 200 feeds the duplexer. Time-frequency subsystem 102 provides analog and digital reference signals for receiver 100, control signal interface 300, and transmitter 200, as known to those skilled in the art. CDMA power control is provided by gain control circuit 104 . In one embodiment of the invention, the control signal interface 300 is a digital signal processor (DSP). On the other hand, the control signal interface may be another circuit capable of performing a gain control function. Control signal interface 300 provides control signals for wireless unit 20 . Receiver 100 provides radio frequency (RF) downconversion and first stage intermediate frequency (IF) downconversion. A digital IF application specific integrated circuit (ASIC) 400 provides a second stage of IF to baseband down conversion, sampling and A/D conversion. Mobile demodulator ASIC 500 searches and correlates digital baseband data from digital IF ASIC 400 to determine pseudoranges, as described in detail below.

Mobile demodulator 500 sends pseudoranges and any voice or data to digital IF modulator 400 . The digital IF modulator 400 performs first-stage IF up-conversion on the data received from the mobile demodulator 500 . These signals are subjected to a second stage of IF upconversion and RF upconversion by the transmitter circuit 200 . These signals are then sent to the base station 10 and processed according to the method of the invention, as described below. It should be noted that preferably a data burst type message (such as Short Message Service (SMS) promulgated by the Telephone Industry Association as defined by industry standard TIA/EIA/IS-67) is provided by the wireless unit 20 to communicate over the wireless unit 20. Location information communicated between unit 20 and BSC 14, such as pseudoranges received by wireless unit 20, is sent to base station 10. On the other hand, the wireless unit 20 can send the newly defined burst type message to the base station 10 .

5 is a block diagram of an exemplary implementation of the receiver, control signal interface, digital IF and mobile demodulator circuit portions of the wireless unit 20 of the present invention. The transmitter portion of the wireless unit 20 is practically the same as that of a conventional wireless unit and therefore will not be described here for brevity. In the preferred embodiment, receiver 100 is implemented via first and second paths 103 and 105, respectively, which are both connected to antenna 92 via first switch 106 and then via diplexer 94. Those skilled in the art will understand that more integration is possible between the two-way communication device and the GPS receiver. On the other hand, two separate receivers with appropriate interfaces can achieve the object of the invention.

The first path 103 downconverts the received CDMA signal and provides a conventional CDMA RF downconverted output signal. The first path 103 includes a low noise amplifier 108 , a first bandpass filter 112 , a first mixer 118 and a second bandpass filter 126 . The second path 105 downconverts GSP signals from the GPS satellites 60, 70, 80 or 90 of FIG. 1 . The second path 105 includes a second low noise amplifier 110 which feeds a third bandpass filter 114 . The output of the bandpass filter 114 is input to the second mixer 120 . The output of the second mixer is fed to a fourth bandpass filter 128 . The first and second mixers are fed by first and second local oscillators 122 and 124, respectively. The first and second local oscillators 122 and 124 operate at different frequencies under the control of a dual phase-locked loop (PLL) 116 . Dual PLLs ensure that each local oscillator 122 and 124 maintains a reference frequency Enables efficient down-conversion of received CDMA signals in the case of the first mixer 118 or received GPS signals in the case of the second mixer 120 . The outputs of the second and fourth bandpass filters 126 and 128 are coupled to a first IF section 130 of conventional design.

The output of IF demodulator 130 is input to second switch 402 in digital IF ASIC 400. The first and second switches 106 and 402 operate under the control of the control signal interface 300 to reverse the direction of the received signal for voice or data output processing by conventional CDMA methods or by the third mixer 404, the fifth band GPS processing by pass filter 406, automatic gain control circuit 408 and analog-to-digital converter 410. The second input to the third mixer 404 is the local oscillator output. Mixer 404 converts the used signal to baseband. The filtered, gain-controlled signal is fed to an analog-to-digital converter (“A/D”) 410 . The output of A/D 410 includes a first digital stream of in-phase (I) components and a second digital stream of quadrature components (Q). These digitized signals are fed to a digital signal processor 520 which processes the GPS signals and outputs the pseudorange information needed for positioning.

In another embodiment of the invention, the outputs from the two bandpass filters 126, 128 are fed to a baseband application specific integrated circuit (ASIC), which converts the IF frequency signal output from the baseband filters 126, 128 to baseband , and outputs a stream of digital values representing the quadrature and in-phase baseband signals. These signals are then used in the searcher. The searcher is basically the same as that traditionally used in CDMA modulators. However, the searcher used is preferably programmable so as to allow the searcher to search for PN codes associated with CDMA signals transmitted from the base station or PN codes associated with GPS satellites. The searcher distinguishes between CDMA channels when receiving a CDMA signal from a base station, and determines the GPS satellite that is transmitting the received GPS signal when in GPS mode. In addition, once the GPS signal is acquired, the searcher indicates the time offset associated with the PN code in essentially the conventional manner to determine the pseudorange associated with the satellite from which the signal was received, as is known to those skilled in the art known.

Those skilled in the art will understand that double transform processing (as shown in Figure 5) or alternatively single transform and IF sampling techniques can be used to generate the required I and Q samples. Furthermore, the structure of the embodiment shown in FIG. 5 can be changed in various ways without affecting the operation of the present invention. For example, a traditional programmable processor can be used instead of a DSP as shown in FIG. 5 . If the rate of data passing through the system is such that no buffers are required, then memory 510 is not required. Under certain conditions, the bandpass filter 406 and the automatic gain control circuit 408 can be omitted, implemented or changed using digital or analog techniques. Various other changes may be made to the structure shown in FIG. 5 without changing the invention. Furthermore, it should be noted that another embodiment may have greater or lesser sharing of hardware and software resources between the GPS and the wireless receiver.

Figure 6 is a high level block diagram of elements of a communication system incorporating the present invention. In operation, BSC 14 requests GPS information from control processor 62 (FIG. 3) in base station 10 in accordance with the method of the present invention. This information includes, but is not limited to, all satellites currently seen by the GPS transceiver 74 (FIG. 3), their elevation angles, Doppler shifts, and pseudoranges at a particular time. Note that the GPS receiver at base station 10 has the latest information on the location, frequency and PN offset of each satellite in view, since it always tracks all satellites in view. On the other hand, base station 10 may transmit data corresponding to a subset of those satellites visible to wireless unit 20, assuming base station 10 stores stored information regarding road widths and heights of surrounding buildings. That is, if the base station 10 has the capability to determine one or more satellites that are not visible to the wireless unit, then the base station 10 does not transmit information about those satellites that are blocked.

It should be noted that conventional GPS receivers record the time of reception of satellite signals relative to the receiver's internal GPS clock. However, the receiver's internal GPS clock is not precisely synchronized with "true" GPS time. Therefore, the receiver cannot know the exact moment in "true" GPS time when the satellite signal was received. Afterwards, the navigation algorithm corrects this error with a fourth satellite. That is, a conventional GPS receiver requires only three satellites to accurately determine the receiver's position if the clock in the receiver is precisely synchronized with the clock in each satellite. However, since the receiver clock is not precisely synchronized with the satellite clock, additional information is required. This additional information is provided by noting the moment at which the receiver received the signal from the fourth satellite. This can be understood by the reminder that there are four equations (i.e., one equation for each of the four satellites) and four unknowns that must be solved for (i.e., the x, y, and z coordinates of the receiver , and the error in the receiver clock). Therefore, for a three-dimensional solution, in a conventional GPS receiver, at least four measurements to four different satellites are required.

Instead, the present system utilizes earth-based stations, which are synchronized with real GPS time. In one embodiment, the station is a CDMA base station. Those skilled in the art will understand that the CDMA base station is synchronized with GPS time. In addition, all wireless units communicating through these CDMA base stations using the CDMA protocol are also synchronized to an offset GPS time that is unique to each wireless unit 20 . The offset in time is equal to the one-way delay due to the radio signal propagating from the base station antenna to the radio unit antenna. This is due to the fact that the wireless unit synchronizes its clock by receiving an indication from the base station of GPS time. However, when the indication reaches the wireless unit, the indication is erroneous by an amount equal to the propagation delay experienced by the signal from the base station to the wireless unit. This propagation delay can be determined by measuring how long it takes a signal to travel between the base station and the wireless unit and back. One-way latency is equal to half the round-trip latency. Various methods of measuring the round trip are available to those skilled in the art.

Additionally, the distance between the base station 10 and the wireless unit 20 may be used to assist in determining the location of the wireless unit 20 . Thus, where there is a direct line of sight (LOS) between the base station 10 and the wireless unit 20, only two satellite range measurements and one base station range measurement are required. In the absence of a direct LOS between the serving base station and the wireless unit, three satellite measurements and one round-trip delay measurement are required to compute the three-dimensional position. Accurate satellite measurements are required to correct for the additional distance introduced by the additional delay due to multipath. The round trip delay is used to correct for clock errors in the wireless unit.

The system described here allows the location of an active CDMA wireless unit to be determined using the Wireless Positioning Function (WPF) 18 (FIG. 6) at any time, as long as the wireless unit 20 is within the radio coverage area of the CDMA network and as long as there are sufficient business quality. The process of determining the location of the wireless unit may be initiated by the wireless unit 20, the network, or an external entity such as an internal location application (ILA) 17, an external location application (ELA) 15 or an emergency service application (ESA) 13. These elements 13, 15 Each element in and 17 can be hardware or software, and they can request and/or receive location information.In one embodiment, ILA 17 is the terminal that is coupled to BSC 14, and it allows operator to directly request and receive information about wireless unit 20 On the other hand, ILA17 is a software application executed by a processor in MSC12.

WPF18 is preferably a conventional programmable processor with the capability to accept raw data received from the radio unit and from the satellites (i.e., pseudoranges to two satellites, distance from the radio unit to the base station, and time correction factors) and The ability to calculate the location of the wireless unit. However, any device capable of receiving information that calculates the location of the wireless unit 20 from such received information and outputs this location determination may be used. For example, WPF 18 may be implemented as an ASIC, discrete logic circuit, state machine, or software application within another network device such as BSC 14 . Furthermore, it should be understood that WPF 18 may be located at base station 10, BSM 14 or within MSC 12. Preferably, WPF 18 is a software application executed by a dedicated processor in communication with BSC 14 . Accordingly, base station 10, BSC 14 and MSC 12 do not need to be extensively modified in order to implement the present invention with conventional components. WPF18, on the other hand, is a software application implemented by a processor within BSC14. WPF 18 preferably communicates with BSC 14 through a communication port similar to that used by conventional billing functions, administrative functions, HLR/VLR functions and other ancillary functions implemented by a processor coupled to a conventional BSC.

Algorithms for calculating position are presented in "Global Positioning System: Principles and Applications" by Parkinson, B.W. and Spilker, J.J. (eds.), Vol. I, American Association of Aeronautical and Space Corporations, Washington DC, 1996. Also, it should be noted that Volume II presents how to perform differential GPS corrections. Those skilled in the art will appreciate that such corrections can be implemented by WPF 18 to accurately calculate the location of the wireless unit.

According to an embodiment of the present invention, a service provider can define a location service according to several conditions (such as capability, security, service distribution, etc.). Location services may support each or a subset of the following services:

(1) Wireless Unit Origination Request (WPF) for positioning.

(2) Network Originated Request (NRP) for positioning.

(3) Location Per Service Instance (PSI): The wireless unit temporarily allows external applications to locate the unit in order to deliver specific services.

(4) Positioning with/without wireless unit identification (PWI/PWO): All wireless units in a defined geographical area will be located. PWI will give the identification and location of these units, while PWO will only give their location.

(5) Positioning in Closed Groups (PCG): Allows the creation of groups in which specific positioning rights can be determined (fleet management). Table 1 Types of positioning services Originator Periodicity On request (single/multiple instances) periodic event trigger wireless unit WPF, PSI, PCG WPF, PCG WPF network PWO PWO NRP/PWO external PWO, PWI, PCG, PSI PWO, PWI, PCG

According to an embodiment of the present invention, wherein the wireless unit 20 initiates a request to determine the location of the wireless unit 20, the wireless unit 20 sends a location request to the MSC 12. MSC 12 validates the request to ensure that wireless unit 20 has subscribed to the requested service type. The MSC 12 then sends a request to the serving BSC 14 to find the location of the wireless unit 20 . The BSC 14 requests positioning assistance information from the base station 10 providing the service. The base station 20 providing the service by transmitting the satellites in view, their Doppler shift, their Doppler rate of change, their pseudorange, their elevation angle, their signal-to-noise ratio (SNR) and A list of round-trip delays (RTDs) between base stations providing traffic, in response to the request. Note that the GPS receiver 74 in the base station 10 continuously tracks the positions of the satellites in view and therefore may have up-to-date information on these parameters. The BSC14 will use each satellite's RTD, pseudorange, satellite elevation, Doppler shift, and Doppler rate of change to calculate the search window center and search window size in time and frequency as follows (see Figure 7):

In the time domain, the center of the search window for the ith space vehicle (“SV _i ”) is equal to the pseudorange between the serving base station 10 and SV _i ,_b in FIG. 7 . The search window size for SV _i is equal to the round trip delay times cos(_i), where cos(_i) is the cosine of the satellite's elevation angle with respect to the Earth's radius originating at the center of the Earth and passing through the receiver.

In the frequency domain, the center of the search window center for _SVi is equal to fo+ _fdi ; where fo equals the carrier frequency of the GPS signal, and fdi equals the Doppler shift of the signal transmitted by SVi. The search window size for SV _i is equal to the frequency uncertainty due to receiver frequency error and Doppler rate of change. The BSC 14 transmits information including satellites in view, search window center, size (time and frequency) and the minimum number of satellites required to determine the wireless unit 20's position.

According to one embodiment, the message to the wireless unit 20 will trigger a retune signal at the wireless unit 20 . The message may also have an "action time" (a specific time in the future when the receiver retunes to the GPS receiver frequency). In response, the wireless unit 20 will activate the first and second switches 106 and 402 at the action time, thereby retuning itself to the GPS frequency. The digital IF ASIC400 changes its PN generator (not shown) to GPS mode and starts searching for all specific satellites.

Once the wireless unit 20 acquires the minimum number of required satellites, it calculates pseudoranges from the GPS clock within the wireless unit 20, retunes to the communication system frequency and compares the pseudorange results and the signal-to-noise ratios measured by the first three satellites to the nearest CDMA pilot search results are sent to BSC14. Pilot search results are required if the unit cannot acquire three satellites and there is no direct line-of-sight path between the serving base station and the wireless unit 20 . However, less than three satellites can be used as long as the round trip delay from another device (such as another base station) is calculated using available information (such as pilot search information). In the prior art, techniques for determining the round-trip delay from pilot search information are known.

The BSC 14 sends the pseudorange measurements made by the wireless unit 20 to the WPF 18 along with the location of the serving base station 10, the corresponding round-trip delay measurement, the considered satellite location (spatial) (relative to a fixed, predetermined reference origin) and differential GPS corrections , where the position of the wireless unit 20 is calculated. The pseudoranges received by BSC 14 from wireless unit 20 and passed to WPF 18 are related to the clock within wireless unit 20 . Therefore, they are erroneous (ie, biased by the round-trip delay between the servicing BTS 10 and the wireless unit 20). FIG. 8 is a diagram showing how WPF 18 corrects local clock bias. In Fig. 8, δ1 represents the pseudorange (half of the round-trip delay) of receiving a signal sent from the base station 10 to the wireless unit 20 (and vice versa), and rm1, rm2 and rm3 are the distances from the wireless unit to the first and second and the pseudoranges of the third selected GPS satellites 60, 70 and 80. These measurements are made relative to a local clock in the wireless unit 20 . However, since the local clock is offset from the real GPS time δ1, the corrected pseudorange is as follows:

ρ1=ρm1+δ1

ρ2=ρm2+δ1

ρ3=ρm3+δ1

The WPF 18 calculates the position of the wireless unit 20 using the above three equations for the position (space) of the three satellites, the position of the serving base station and the corresponding RTD measurements. Note that an RTD is equivalent to knowing precisely the offset of the wireless unit's local clock relative to true GPS time. That is, it is sufficient to solve three range equations in terms of three satellites.

Also note that the minimum number of satellites required can be reduced to two if there is a direct line-of-sight connection between the wireless unit 20 and the base station, so that the distance between the wireless unit 20 and the base station 10 can be directly determined by the distance between the wireless unit 20 and the base station 10. 20 and the base station 10 to determine the RTD. This number can be further reduced if information about other pilots (stations) is available. For example, if the wireless unit 20 communicates with two or more base stations (e.g., soft handoff), neither of which has a direct line of sight to the wireless unit 20, then more than one round trip delay can be calculated, and the two satellites are All that is needed to determine the location of the wireless unit 20. That is, according to five equations (two equations for the two pseudorange measurements associated with the two satellites, two equations for the two base station RTD measurements and one equation for the RTD to the serving base station, it allowing the local clock within the wireless unit 20 to be synchronized with real GPS time). This is useful in situations where GPS satellites are blocked by buildings or trees. Furthermore, it reduces the time to search for GPS satellites. The WPF 18 sends the calculated position to the BSC 14, which sends it to the MSC 12 or directly to the wireless unit 20.

The invention is described with reference to specific embodiments for particular applications. Those familiar with the art and reading this specification will recognize that additional modified applications and embodiments are within its scope. Accordingly, the appended claims cover any and all such applications, modifications and embodiments which fall within the scope of this invention.

Claims (21)

1. the system of the position of a definite mobile wireless transceiver is characterized in that, comprising:

The base station;

Calculate respectively from the signal of first, second and the 3rd satellite transmission device with respect to the Doppler shift of described base station;

Calculate the device of first and second satellites respectively with respect to first group of pseudorange of described base station;

Between described base station and described transceiver, send the device of satellite identification information, Doppler shift information and described pseudorange information;

Be positioned at the device that described transceiver place is used to receive described satellite identification information, Doppler shift information and described pseudorange information from described base station;

Described transceiver respectively and the device of second group of pseudorange between described first and second satellites when being used to utilize the described information that receives from described base station to be identified in constantly T at described mobile wireless transceiver place;

Be used at described mobile wireless transceiver place described transceiver respectively the described second group of pseudorange between described first and second satellites and constantly the temporal information of T send to the device of described base station; With

Being positioned at place, described base station is used for calculating the device of the position of described transceiver in response to the temporal information of described second group of pseudorange and described moment T.

2. the system as claimed in claim 1, it is characterized in that, be positioned at place, described base station and be used for comprising and determine the device of described transceiver from the distance of described base station in response to the described device that the temporal information of described second group of pseudorange and described moment T is calculated the position of described transceiver.

3. system as claimed in claim 2, it is characterized in that, be arranged in described device that place, described base station is used to calculate the position of described transceiver and be included in the position of calculating described transceiver and utilize the device of described transceiver from the distance of described base station.

4. the system as claimed in claim 1 is characterized in that, comprises being positioned at the device that place, described base station is used to discern two best located satellites.

5. the system as claimed in claim 1 is characterized in that, comprises the device of second pattern from first mode switch that influences voice/data communications to the position of determining it described mobile wireless transceiver.

6. the system as claimed in claim 1 is characterized in that, is positioned at the described device that place, described base station is used to calculate the position of described transceiver and comprises:

Utilize described second group of pseudorange calculate described first and second satellites respectively and the device of the 3rd group of pseudorange between the described base station and

Utilize described first and second satellites in the known location of the known location of moment T, described base station, described the 3rd group of pseudorange with postpone to determine the device of the described position of described transceiver from the time of arrival that described mobile wireless transceiver sends to described signal of base station.

7. system as claimed in claim 6, it is characterized in that, the described device that calculates the described position of described transceiver comprises first ball of finding out first first radius in described first and second satellites, in described first and second satellites second second radius second ball and around the device of the intersection point of the 3rd ball of the 3rd radius of described base station.

8. the system as claimed in claim 1, it is characterized in that, the described device that calculates the described position of described transceiver comprises first ball of finding out first first radius in described first and second satellites, in described first and second satellites second second radius second ball and around the device of the intersection point of the 3rd ball of the 3rd radius of described base station.

9. the system of the position of a definite mobile wireless transceiver is characterized in that, comprising:

The base station;

Be positioned at the device that place, described base station is used to discern first and second GPS satellite;

Calculate respectively from the signal of described first and second satellite transmissions device with respect to the Doppler shift of described base station;

Calculate the device of described first and second satellites respectively with respect to first group of pseudorange of described base station;

Satellite identification information, Doppler shift information and described pseudorange information are sent to the device of described transceiver from described base station;

Be positioned at the device that described transceiver place is used to receive described satellite identification information, Doppler shift information and described pseudorange information from described base station;

Described transceiver respectively and the device of the described second group of pseudorange between described first and second satellites when being used to utilize the described information that receives from described base station to be identified in time T at described mobile wireless transceiver place;

Be used at described mobile wireless transceiver place described transceiver respectively and between described first and second satellites second group of pseudorange and constantly the temporal information of T send to the device of described base station together; With

Be positioned at place, described base station and calculate the device of the position of described transceiver in response to the temporal information of described second group of pseudorange and described moment T, this calculation element comprises:

Determine the device of described transceiver from the distance of described base station; With

In the position of calculating described transceiver, utilize the device of described transceiver from the distance of described base station.

10. system as claimed in claim 9 is characterized in that, comprises the device of second pattern from first mode switch that influences voice/data communications to the position of determining it described mobile wireless transceiver.

11. system as claimed in claim 9 is characterized in that, is positioned at the described device that place, described base station is used to calculate the position of described transceiver and comprises:

Utilize described second group of pseudorange to calculate described first and second satellites respectively and the device of the 3rd group of pseudorange between the described base station; With

Utilize described first and second satellites in the position of the known location of moment T, described base station, the 3rd group of pseudorange and postpone to determine the device of the position of described transceiver from the time of arrival that described mobile wireless transceiver sends to described signal of base station.

12. system as claimed in claim 11, it is characterized in that, the described device that calculates the position of described transceiver comprise find in two satellites first first radius first ball, second second radius in two satellites second ball and around the device of the intersection point of the 3rd ball of the 3rd radius of described base station.

13. system as claimed in claim 9, it is characterized in that, the described device that calculates the position of described transceiver comprises first ball that finds first first radius in two satellites, in two satellites second second radius second ball and around the device of the intersection point of the 3rd ball of the 3rd radius of described base station.

14. the method for the position of a definite mobile wireless transceiver is characterized in that, comprises the following steps:

Calculate respectively from the signal of first and second satellite transmissions Doppler shift with respect to the base station;

Calculate the first group pseudorange of described first and second satellites respectively with respect to described base station;

Satellite identification information, Doppler shift information and described pseudorange information are sent to described transceiver from described base station;

In described satellite identification information, Doppler shift information and the described pseudorange information of described transceiver place reception from described base station;

Described transceiver respectively and second group of pseudorange between described first and second satellites when described information that utilization receives from described base station was identified in constantly T;

Described transceiver respectively and the described second group of pseudorange between described first and second satellites and constantly the temporal information of T send to described base station together; With

The position of calculating described transceiver in response to described second group of pseudorange and described temporal information.

15. method as claimed in claim 14, it is characterized in that the described step of calculating the position of described transceiver in response to the temporal information of described second group of pseudorange and described moment T comprises the step of definite described transceiver from the distance of described base station.

16. method as claimed in claim 15 is characterized in that, the described step of calculating the position of described transceiver is included in the step of utilizing the distance between described transceiver and the described base station in the position of calculating described transceiver.

17. method as claimed in claim 14 is characterized in that, comprises the step of discerning two best located satellites.

18. method as claimed in claim 14 is characterized in that, the step of second pattern described mobile wireless transceiver from first mode switch that influences voice/data communications to the position of determining it.

19. method as claimed in claim 14 is characterized in that, the described step of calculating the position of described transceiver comprises the following steps:

Calculate respectively and the 3rd group of pseudorange between the described base station with described second group of pseudorange at described first and second satellites; With

Utilize described two satellites at known location, the 3rd group of pseudorange of moment T with send to the position that postpones to determine described transceiver time of arrival of described signal of base station from described mobile wireless transceiver.

20. method as claimed in claim 19, it is characterized in that, the described step of calculating the position of described transceiver comprises first ball that finds first first radius in two satellites, in two satellites second second radius second ball and around the step of the intersection point of the 3rd ball of the 3rd radius of described base station.

21. method as claimed in claim 14, it is characterized in that, the described step of calculating the position of described transceiver comprises first ball that finds first first radius in two satellites, in two satellites second second radius second ball and around the step of the intersection point of the 3rd ball of the 3rd radius of described base station.

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